Product differentiation that makes the product better for some consumers and worse for others is

A) always welfare decreasing.
B) vertical differentiation.
C) horizontal differentiation.
D) never undertaken by firms.

Horizontal differentiation refers to differences in products that make them better for some consumers and worse for others based on personal preferences, rather than quality or price. This contrasts with vertical differentiation, where product differences are objectively better or worse, such as in quality or performance.